The present invention relates to a magnetic recording media. More particularly, it relates to a coated magnetic recording media, such as a magnetic recording tape, including a magnetic coating exhibiting low abrasivity with reliable performance.
Magnetic recording media, such as magnetic recording tapes, enjoy wide use and popularity. Such media has evolved to provide increased recording density or capacity per unit volume, reduced average surface roughness and surface roughness variability, reduced electromagnetic amplitude degradation caused by roughness and other factors, and increased reliability, as measured by e.g., read and write error rate increases over extended periods of use.
In general terms, magnetic recording media generally comprise a magnetic coating formed onto at least one side of a non-magnetic substrate (e.g., a film for a magnetic recording tape application). With certain designs, the magnetic coating (or “front coating”) is formed as a single layer. In an effort to reduce a thickness of this magnetic recording layer, a more recent approach is to form the front coating as a dual layer construction, including a support layer (or “lower layer”) on the substrate and a reduced-thickness magnetic layer (or “upper layer”) formed directly on the support or lower layer. With this construction, the lower layer is typically non-magnetic or substantially non-magnetic, generally comprised of a non-magnetic powder and a binder. Conversely, the upper layer comprises a magnetic metal particle powder or pigment dispersed in a polymeric binder. Finally, with magnetic recording tape, a backside coating is applied to the other side of the non-magnetic substrate in order to improve the durability, conductivity, and tracking characteristics of the media.
Linear Tape Open (LTO) technology seeks to provide open-format, high-performance tape storage products that enhance reliability and versatility in, for example, the network tape storage environment. LTO technology, being open-format, provides users with multiple sources of product and media, and enables compatibility between the offerings of different venders. The ULTRIUM format is a high-capacity implementation of LTO technology. Other technologies are well-established and known in the art, for example, the Digital Linear Tape Series formats including DLT4000, DLT7000, and DLT8000 (also known as DLT4, DLT7, and DLT8) drives and media. Detail technical descriptions of each of these format generations are available from, for example, the European Computer Manufacturers Association (ECMA) and the American National Standards Institute (ANSI). DLT magnetic tape cartridges and drives are available in many systems and provide tape back-up capabilities, for example.
Regardless of the exact formatting requirements, the magnetic coating includes an abrasive additive. Media abrasivity is controlled by the selection of the type and amount of abrasive additive, as well as the processing conditions. Processing conditions include compounding the dispersion, coating and drying the dispersion, calendering the resultant magnetic recording medium and burnishing the same. The purpose of adding the abrasive material to the dispersion is that the abrasive material is needed to keep read/write heads clean. However, the abrasive material also leads to degradation of the read/write head over time. Thus, a balance exists between the desired head cleaning characteristics of the abrasive and the undesired head degradation that the abrasive causes.
Regardless of format, data reliability is a function of “spacing” signal amplitude between the read/write head and the magnetic recording medium during use (i.e., degradation of playback signal strength). This spacing loss can be the result of excessive abrasivity, wherein the active elements of the read/write head are eroded away from the average media plane of travel. In effect, the point at which the magnetic recording media's abrasivity causes read/write head erosion defines an upper abrasivity limit. Conversely, spacing loss can be due to insufficient abrasivity, which allows the build-up of debris on and around the active elements of the read/write head, forcing the media plane of travel away from the active elements. The point at which the magnetic recording media's abrasivity allows for the accumulation of excessive debris effectively defines the lower abrasivity limit of the particular media/format. Notably, the evolution of magnetic recording media technology has required an increase in the available recording density. For example, the DLT4 format operates at a recording density of 55 kfci. This and other high-recording density formats are less tolerant to spacing loss (as dictated by the Wallace equation). Thus, as recording density increases for DLT and other high-recording density formats, the upper and lower recording medium abrasivity limits are typically forced to converge, reducing the functional margin between these limits.
In light of the above, when developing the magnetic coating for a magnetic recording medium, manufacturers typically start with a formulation/processing technique that generates a high abrasivity level (i.e., above the expected upper abrasivity level). Through various testing, the formulation and/or processing technique(s) is altered so as to lower the abrasivity level to a point whereby potential erosion of the read/write head during use is within acceptable limits. In other words, the magnetic coating is modified so as to approximate the upper abrasivity limit. At this point, it is assumed that because the abrasivity level is well above the theoretical lower abrasivity limit, performance reliability (due to insufficient abrasivity) is not at issue. However, read/write head wear issues may still arise. That is to say, even at or near the upper abrasivity limit, the so-formed magnetic recording medium may cause undesirable read/write head erosion during use. Thus, a need exists for magnetic recording media having a magnetic coating abrasivity that more closely approximates the theoretical lower abrasivity limit while exhibiting performance reliability comparable to other, similarly-formatted products.